A washer is a thin plate (typically disk-shaped) with a hole (typically in the middle) that is normally used to distribute the load of a threaded fastener. Other uses are as a spacer, spring (belleville washer, wave washer), wear pad, preload indicating device, and locking device. Rubber washers are also used in taps (valves) where they form the seal that shuts off the flow of liquid or gas. Rubber or silicone washers may also be used to reduce vibration when fastening fans to computer cases. Usually washers have OD (outer diameter) about twice their ID (inner diameter).
Washers are usually metal or plastic. High quality capscrews require hardened steel washers to prevent the loss of pre-load due to Brinelling after the torque is applied. Rubber or fiber gaskets used in taps to stop the flow of water are sometimes referred to colloquially as washers; while they may look similar, however, washers and gaskets are usually designed for different functions and made differently.
Washers are also important for preventing galvanic corrosion, particularly by insulating steel screws from aluminum surfaces.
Types of washers
rondelle in German: Unterlegscheibe
rondelle in Spanish: Arandela
rondelle in Persian: واشر
rondelle in French: Rondelle (mécanique)
rondelle in Dutch: Ring (schroef)
rondelle in Japanese: 座金
rondelle in Polish: Podkładka (technika)
rondelle in Portuguese: Arruela
rondelle in Romanian: Şaibă
rondelle in Russian: Шайба (деталь)
rondelle in Finnish: Aluslaatta
rondelle in Swedish: Bricka (förbandsteknik)
O, annular muscle, annulus, areola, aureole, chaplet, circle, circuit, circumference, circus, closed circle, corona, coronet, crown, cycle, diadem, discus, disk, eternal return, fairy ring, garland, glory, halo, lasso, logical circle, loop, looplet, magic circle, noose, orbit, radius, ring, round, roundel, saucer, sphincter, vicious circle, wheel, wreath